Catalytic Activity For Ethylene Polymerization Research Articles

Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate): Synthesis, characterization, and their catalytic behaviors for ethylene polymerization

AbstractA series of 6‐(benzimidazol‐2‐yl)‐N‐organylpyridine‐2‐carboxamide were synthesized and transformed into 6‐benzimidazolylpyridine‐2‐carboxylimidate as dianionic tridentate ligands. Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride (C1) and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate) (C2–C8) were synthesized in acceptable yields. These complexes were systematically characterized by elemental and NMR analyses. Crystallographic analysis revealed the distorted octahedral geometry around titanium in both complexes C1 and C4. Using MAO as cocatalyst, all complexes exhibited from good to high catalytic activities for ethylene polymerization. The neutral bis(6‐benzimidazolylpyridine‐2‐carboxylimidate)titanium (C2–C8) showed high catalytic activities and good stability for prolonged reaction time and elevated reaction temperature; however, C1 showed a short lifetime in catalysis as being observed at very low activity after 5 min. The elevated reaction temperature enhanced the productivity of polyethylenes with low molecular weights, whereas the reaction with higher ethylene pressure resulted in better catalytic activity and resultant polyethylenes with higher molecular weights. At higher ratio of MAO to titanium precursor, the catalytic system generated better activity with producing polyethylenes with lower molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3411–3423, 2008

Metallocenes in ethylene polymerization studied by cyclic and differential pulse voltammetry

The relationship between redox characteristics and catalytic activity in ethylene polymerization, with methylaluminoxane (MAO) as the cocatalyst, was evaluated for a series of homogeneous metallocenes (Cp2ZrCl2, (MeCp)2ZrCl2, (nBuCp)2ZrCl2, (iBuCp)2ZrCl2, (tBuCp)2ZrCl2, Cp2TiCl2, Cp2HfCl2, Et(Ind)2ZrCl2, Et(IndH4)2ZrCl2 and MeSi2(Ind)2ZrCl2). Catalytic activity is discussed in terms of the coordination sphere and metal center of the metallocene and compared with their electrochemical behavior in the presence of ethylene and MAO. The resulting polyethylenes were analyzed by GPC. The catalytic activity in the ethylene polymerization reaction is discussed in terms of half-life (t1/2) and electrochemical gap of the metallocene species.

Functional polyethylene composites prepared via polymerization of ethylene with opal‐immobilized zirconocene complex

AbstractAn opal‐supported zirconocene complex (OC) was prepared and employed to prepare functional polyethylene composite for the first time through in situ polymerization of ethylene. The formation mechanism of anion relating to opal was explained and the values of anions released from pristine opal and that contained in the as‐fabricated polyethylene composites were detected. The OC exhibited high catalytic activities in ethylene polymerization with methylaluminoxane (MAO) the cocatalyst. In addition to higher viscosity‐average molecular weights (Mη), experimental results also showed that the resulting polyethylene composites possessed improved anion‐releasing capacity in comparison with pristine opal in addition to increased tensile strength, Young's modulus, and onset decomposition temperature (Tonset) relative to neat polyethylene due to highly uniform dispersion of opal in polyethylene matrix. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Synthesis and characterization of a series of 2‐aminopyridine nickel(II) complexes and their catalytic properties toward ethylene polymerization

AbstractA series of 2‐aminopyridine Ni(II) complexes bearing different substituent groups {(2‐PyCH2NAr)NiBr, Ar = 2,4,6‐trimethylphenyl (3a), 2,6‐dichlorophenyl (3b), 2,6‐dimethylphenyl (3c), 2,6‐diisopropylphenyl (3d), 2,6‐difluorophenyl (3e); (2‐PyCH2NHAr)2NiBr2, Ar = 2,6‐diisopropylphenyl (4a)} have been synthesized and investigated as precatalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight branched polymers as well as short‐chain oligomers were simultaneously produced with these complexes. Enhancing the steric bulk of the ortho‐aryl‐substituents of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. With ortho‐haloid‐substitution, the catalysts afforded a product with low polymer/oligomer ratio (3b) and even only oligomers (3e) in which C14H28 had the maximum content. Compared with complex 3d containing ionic ligand, complex 4a containing neutral ligand exhibited obviously low catalytic activity for ethylene polymerization. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and 13C NMR spectrogram. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1618–1628, 2008

Synthesis, structures, and catalytic properties for ethylene polymerization of bridged [η 5,η 1-C 5H 4CHPhArO]TiCl 2 complexes

A number of bridged half-sandwich titanium complexes [η 5:η 1-2-C 5H 4CHPh-4-R 1-6-R 2C 6H 2O]TiCl 2 [R 1 = H ( 5), Me ( 6), t Bu ( 7, 8); R 2 = H ( 6, 7), t Bu ( 5, 8)] were synthesized from the reaction of their corresponding trimethylsilyl substituted ligand precursors 2-Me 3SiC 5H 4CHPh-4-R 1-6-R 2C 6H 2OSiMe 3 [R 1 = H ( 1), Me ( 2), t Bu ( 3, 4); R 2 = H ( 2, 3), t Bu ( 1, 4)] with TiCl 4 in hexane. All new complexes were characterized by 1H and 13C NMR spectroscopy. Molecular structures of complexes 5 and 8 were determined by single crystal X-ray diffraction analysis. Upon activation with Al i Bu 3/Ph 3CB (C 6F 5) 4, complexes 5– 8 exhibit reasonable catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing polyethylene and poly(ethylene-co-1-hexene) with moderate molecular weights.

Synthesis of Titanatranes Containing Bis(aryloxo)‐(alkoxo)amines and their Use in Catalysis for Ethylene Polymerization

AbstractSyntheses of titanatranes containing [(O‐2,4‐Me2C6H2‐6‐CH2)2‐{O(CH2)nCH2}]N3− (n = 1,2) have been explored. Catalytic activity for ethylene polymerization by Ti2(OiPr)2{[(O‐2,4‐Me2C6H2‐6‐CH2)2(µ2‐OCH2‐CH2)]N}2 (1a) ‐ MAO catalyst increased at high temperature; the activity also increased upon addition of AlMe3. Ti(O‐ 2,6‐iPr2C6H3){[(O‐2,4‐Me2C6H2‐6‐CH2)2(OCH2CH2)]N} (1c) showed higher activity than 1a under the same conditions. Ti{[(O‐2,4‐Me2C6H2‐6‐CH2)2(HOCH2CH2CH2)]N}2 was isolated from the reaction of Ti(OiPr)4 with bis(2‐hydroxy‐3,5‐dimethylbenzyl)‐propanolamine; the structure was determined by X‐ray crystallography.

Synthesis of Half-Titanocenes Containing Phenoxy-imine Ligands and Their Use as Catalysts for Olefin Polymerization

Various half-titanocenes containing phenoxy-imine ligands of the type Cp‘TiCl2[O-2-R1-6-(R2NCH)C6H3] [Cp‘ = Cp* (C5Me5) and R1, R2 = Me, 2,6-iPr2C6H3 (1); tBu, 2,6-iPr2C6H3 (2); Me, tBu (3); tBu, tBu (4); Cp‘ = 1,2,4-Me3C5H2 and R1, R2 = Me, 2,6-iPr2C6H3 (5); Cp‘ = Cp and R1, R2 = Me, 2,6-iPr2C6H3 (6); Me, tBu (7)] were prepared by reaction of Cp‘TiCl3 with LiO-2-R1-6-(R2NCH)C6H3 that were prepared in situ by treating the corresponding phenol with n-BuLi. Cp*TiMe2[O-2-Me-6-{(2,6-iPr2C6H3)NCH}C6H3] (8) was prepared from Cp*TiMe3 by treating with 2-Me-6-{(2,6-iPr2C6H3)NCH}C6H3OH in n-hexane, and the reaction with [PhN(H)Me2][B(C6F5)4] was also explored. Structures for 1−3 and 5−8 were determined by X-ray crystallography, and the imino nitrogen in the phenoxy-imine ligand was not coordinated to Ti in all cases; the bond angles for Ti−O−C(Ph) were affected by substituents in both cyclopentadienyl and phenoxy-imine ligands. The catalytic activities for ethylene polymerization and syndiospecific styrene polymerization using 1−7−MAO catalyst systems were highly affected by the substituents in both cyclopentadienyl and phenoxy-imine ligands; the Cp* analogues (3, 4) exhibited notable activities for ethylene polymerization, whereas the Cp analogues (6, 7) showed significant activities for syndiospecific styrene polymerization. The Cp analogue 6 was also an effective catalyst precursor for copolymerization of ethylene with norbornene.

Bis(pyrazolyl)pyridine vanadium(III) complexes as highly active ethylene polymerization catalysts

The synthesis, characterization and catalytic activity in ethylene polymerization of novel mononuclear vanadium complexes bearing N ∧ N ∧ N-tridentate (pyrazolyl-pyridine) ligands are described. With AlEtCl 2 as co-catalyst, complexes 1 and 2 produce single-site catalysts that polymerized ethylene affording high density polyethylene with fairly narrow molecular weight distribution.

α‐olefin homopolymerization and ethylene/1‐hexene copolymerization catalysed by novel ansa‐group IV complexes/MAO system

AbstractThe catalytic properties of a set of ansa‐complexes (R‐Ph)2C(Cp)(Ind)MCl2 [R = tBu, M = Ti (3), Zr (4) or Hf (5); R = MeO, M = Zr (6), Hf (7)] in α‐olefin homopolymerization and ethylene/1‐hexene copolymerization were explored in the presence of MAO (methylaluminoxane). Complex 4 with steric bulk tBu group on phenyl exhibited remarkable catalytic activity for ethylene polymerization. It was 1.6‐fold more active than complex 11 [Ph2C(Cp)(Ind)ZrCl2] at 11 atm ethylene pressure and was 4.8‐fold more active at 1 atm pressure. The introduction of bulk substituent tBu into phenyl groups not only increased the catalytic activity greatly but also enhanced the content of 1‐hexene in ethylene/1‐hexene copolymerization. The highest 1‐hexene incorporation was 25.4%. In addition, 4 was also active for propylene and 1‐hexene homopolymerization, respectively, and low isotactic polypropylene (mmmm = 11.3%) and isotactic polyhexene (mmmm = 31.6%) were obtained. Copyright © 2007 John Wiley & Sons, Ltd.

Facile Formation of Hexacyclic [Al3O2Cl] Aluminum and Alkoxide‐Bridged Titanium Complexes: Reactions of AlMe3 with [Ti(L)Cl2] [L = 2,2′‐Methylenebis(6‐tert‐butyl‐4‐methylphenolato)

AbstractThe titanium dichloride complex [(L)TiCl2] [L = 2,2′‐methylenebis(6‐tert‐butyl‐4‐methylphenolato)] (1) reacted with trimethylaluminum (AlMe3) in a 1:2 ratio to give a trimetallic aluminum complex of the composition [(L)(AlMe2)3(μ‐Cl)] (2) with a symmetric six‐membered ring [Al3(μ2‐O)2(μ2‐Cl)] and a four‐coordinate aluminum center in the solid state. The reaction of 1 equiv. AlMe3 gave [(L)TiMeCl] (3), which could absorb O2 gas to afford the oxygen‐insertion product [{(L)TiCl}2(μ‐OMe)2] (4) with a five‐coordinate metal center. Upon reaction of H2L with AlMe3, the binuclear, four‐coordinate adduct [{(L)AlMe}2] (5) was formed. Complex 4 supported on MgCl2 and activated with aluminum alkyls reveals high catalytic activity for ethylene polymerization to produce polymers with molecular weight distributions of ca. 3.1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis of Half-Titanocenes Containing Aryloxide Ligands Attached to the ROMP Polymer Chain End: Unique Catalyst Precursors for Ethylene (Co)polymerization

Half-titanocenes containing aryloxide ligands immobilized on the chain end of ring-opened poly(norbornene)s, (C5Me5)TiMe2[O-2,6-R2C6H2-4-CH{CH-(1,3-cyclo-C5H8)-CH}nCHCMe2Ph] [R = H (1), Me (2), iPr (3)], prepared by living ring-opening metathesis polymerization (ROMP) by Mo(N-2,6-iPr2C6H3)(CHCMe2Ph)(OtBu)2, have been prepared and identified by 1H and 13C NMR spectra, elemental analysis, and X-ray photoelectron spectroscopy. These complexes showed high catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO) cocatalyst, and the effect of the substituent on the aryloxide on both the activity and molecular weight of the resultant polymer was the same as that using nonsupported (C5Me5)TiCl2(O-2,6-R2C6H3) (R = H, Me, iPr). Complex 3 showed both notable catalytic activities and efficient 1-hexene incorporation with the same monomer reactivity ratio as nonsupported (C5Me5)TiCl2(O-2,6-iPr2C6H3) (3‘) for ethylene/1-hexene copolymerization in the presence of MAO.

Synthesis and Crystal Structure of a Zirconium Complex Containing Germanolato Ligands and Its Catalytic Activity for Ethylene Polymerization

Abstract A dialkylbis(germanolato)zirconium complex was synthesized by taking advantage of a novel bowl-shaped germanol as the ligand source, presenting the first example of a zirconium complex containing germanolato ligands. The bis(germanolato) complex as well as the analogous bis(silanolato) complex was found to exhibit catalytic activity for ethylene polymerization.

Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes–MAO catalyst systems: Structural analysis for Cp ∗TiCl 2(N [dbnd]CPh 2)

Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp′TiCl 2[N C(R 1)R 2] [Cp′ = Cp ( 1), C 5Me 5 (Cp ∗, 2); R 1,R 2 = t Bu, t Bu ( a), t Bu,Ph ( b), Ph,Ph ( c)]–methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl 2[N C( t Bu)Ph] ( 1b) CpTiCl 2(N CPh 2) ( 1c), and Cp ∗TiCl 2(N CPh 2) ( 2c) were prepared and identified; the structure of Cp ∗TiCl 2(N CPh 2) ( 2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the order: 1a > 1b > 1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distributions for resultant (co)polymers prepared by 1b, c and by 2c–MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl 2(N C t Bu 2) ( 1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.

Titanium(IV) complexes with monocyclopentadienyl and phenoxy-alkoxo ligands: Synthesis, structures and catalytic properties for ethylene polymerization

Three monochlorotitanium complexes Cp′Ti(2,4- t Bu 2-6-(CPh 2O)C 6H 2O)Cl [Cp′ = η 5-C 5H 5 ( 2), η 5-C 5(CH 3) 5 ( 3), η 5-C 5H 2Ph 2CH 3 ( 4)] have been synthesized in high yields (>90%) by the reaction of corresponding Cp′TiCl 3 with the dilithium salt of ligand 2,4- t Bu 2-6-(CPh 2OH)C 6H 2OH ( 1). When activated by [Ph 3C] +[B(C 6F 5) 4] − and Al i Bu 3, complexes 2– 4 exhibit reasonable catalytic activity for ethylene polymerization, producing polyethylenes with moderate molecular weights and melting points. Addition of excess water to complex 2 gave the oxo-bridged complex [Ti(η 5-C 5H 5)(2,4- t Bu 2-6-(CPh 2O)C 6H 2O)] 2O ( 5). Complexes 4 and 5 were characterized by single crystal X-ray diffraction.

Synthesis, structures and catalytic properties of stable oxo-bridged half-sandwich titanium complexes

Hydrolysis of 1,2-diphenyl-4-R-cyclopentadienyl titanium trichloride (R = Me ( 1), n-Bu ( 2)) affords the corresponding oxo-bridged monocyclopentadienyl titanium compounds (1,2-Ph 2-4-R-CpTiCl 2) 2(μ-O) (R = Me ( 3), n-Bu ( 4)), new dinuclear species. The molecular structures of complexes 3 and 4 have been confirmed by single-crystal X-ray diffraction. Both complexes have been characterized by elemental analysis, 1H and 13C NMR spectroscopy. When activated with Al( i Bu) 3 and Ph 3 C + B ( C 6 F 5 ) 4 - , complexes 3 and 4 show reasonable catalytic activity for ethylene polymerization, producing polyethylenes with moderate molecular weights, and upon activation with methylaluminoxane (MAO), complexes 3 and 4 exhibit high catalytic activity and syndiospecificity for the polymerization of styrene.

Arene-Bridged Salicylaldimine-Based Binuclear Neutral Nickel(II) Complexes: Synthesis and Ethylene Polymerization Activities

A series of novel m-arene-bridged salicylaldimine-based binuclear neutral nickel(II) complexes (2,4,6-(R2)3C6H-1,3-[NCH-4-X-6-R1C6H2ONi(Ph)(PPh3)]2 (3a−i: R1, R2, X = Me, Me, H (3a), tBu, Me, H (3b), Me, Et, H (3c), tBu, Et, H (3d), H, iPr, H (3e), Me, iPr, H (3f), tBu, iPr, H (3g), Ph, iPr, H (3h), NO2, iPr, NO2 (3i), H, iPr, NO2 (3j)) are synthesized. The structure of complex 3h is further confirmed by an X-ray diffraction study showing that the two Ni centers adopt an unsymmetrical, distorted square planar geometry. In the presence or absence of the phosphine scavenger Ni(COD)2, complexes 3a−j show high catalytic activities for ethylene polymerization. The effect of substituents on ethylene polymerization is significant. The introduction of an electron-withdrawing group to the ligand framework improves the catalytic activity significantly. The influence of polymerization temperature, polymerization time, and catalyst concentration on the activities of ethylene polymerization is also investigated. Highly branched polyethylenes (46−127 branches per 1000 carbon atoms) with moderate molecular weights (Mη = (1.0−169) × 104) and narrow molecular weight distributions (Mw/Mn = 2.3−2.4) are obtained by using complexes 3a−j as catalysts with or without a phosphine scavenger. In the presence of a polar solvent such as THF or Et2O, complex 3h polymerizes ethylene as a single-component catalyst. In comparison to the corresponding mononuclear Ni catalysts, the binuclear Ni catalysts generally show higher thermal stability, and complexes 3a, 3c, 3e, and 3f, which feature small R1 substituents, are capable of acting as single-component ethylene polymerization catalysts.

Asymmetric binuclear titanocenes linked by alkyl benzyl ethers: Synthesis, characterization and use as catalysts for ethylene polymerization

A series of novel asymmetric binuclear titanocenes linked with alkyl benzyl ethers p-[(C 5H 5TiCl 2)C 5H 4CH 2]C 6H 4O(CH 2) n [C 5H 4(TiCl 2C 5H 5)] ( n = 2–5) ( 13– 16) have been synthesized by treating p-(LiC 5H 4CH 2)C 6H 4O(CH 2) n (C 5H 4Li) ( n = 2–5) ( 9– 12) with C 5H 5TiCl 3. The new complexes have been characterized by elemental analysis and NMR spectra. Their catalytic activity for ethylene polymerization was investigated in the presence of aluminoxane (MAO). The results show that 13– 16 are efficient catalysts for producing polyethylene (PE) with a broad molecular weight distribution (MWD). Their catalytic activity is highly dependent on the length of the alkyl chain and the polymerization conditions. A longer alkyl chain increases the catalytic activity, whereas the molecular weight of the produced polyethylene decreases.

New o-methoxyphenylcyclopentadienylchromium (III) complexes: Synthesis, structures and catalytic properties for ethylene polymerization

Two new ligands 1-(2-methoxyphenyl)-3,4-diphenylcyclopentadiene ( 1) and 1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadiene ( 2), as well as their corresponding cyclopentadienylchromium complexes η 5-1-(2-methoxyphenyl)-3,4-diphenylcyclopentadienyl chromium dichloride ( 3) and η 5-1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadienyl chromium dichloride ( 4) were synthesized and characterized. Molecular structures of 3 and 4 were determined by single-crystal X-ray diffraction. Complexes 3 and 4 were tested as catalyst precursors for ethylene polymerization. When activated with Al( i Bu) 3 and Ph 3 C + B ( C 6 F 5 ) 4 - , complex 3 shows reasonable catalytic activity while 4 exhibits high catalytic activity for ethylene polymerization. The effects of temperature and Al/Cr ratio on the catalytic activity were studied. The molecular weight and melting temperature of the produced polyethylenes were determined.

Chromium complexes ligated by 2-carbethoxy-6-iminopyridines: Synthesis, characterization and their catalytic behavior toward ethylene polymerization

The titled chromium complexes ( C1– C6) were prepared by the reaction of CrCl 3(THF) 3 with the corresponding 2-carbethoxy-6-iminopyridines ( L1– L6) in dichloromethane. All the complexes were characterized by IR spectroscopy and elemental analysis. The unambiguous solid-state structures of C1, C3 and C5 were determined by X-ray crystallography. The chromium core was found to be coordinated by a molecule of 2-carbethoxy-6-iminopyridine and three atoms of chlorine to form a distorted octahedral coordination geometry. Activated with ethylaluminum dichloride (EtAlCl 2), these complexes showed notable catalytic activities for ethylene polymerization. The nature of the ligands and reaction parameters affected the properties of the resultant polyethylenes.

Synthesis of novel zirconium complexes bearing mono‐Cp and tridentate Schiff base [ONO] ligands and their catalytic activities for olefin polymerization

AbstractA series of novel zirconium complexes {R2Cp[2‐R1‐6‐(2‐CH3OC6H4NCH)C6H3O]ZrCl2 (1, R1 = H, R2 = H, 2: R1 = CH3, R2 = H; 3, R1 = tBu, R2 = H; 4, R1 = H, R2 = CH3; 5, R1 = H, R2 = n‐Bu)} bearing mono‐Cp and tridentate Schiff base [ONO] ligands are prepared by the reaction of corresponding lithium salt of Schiff base ligands with R2CpZrCl3·DME. All complexes were well characterized by 1H NMR, MS, IR and elemental analysis. The molecular structure of complex 1 was further confirmed by X‐ray diffraction study, where the bond angle of ClZrCl is extremely wide [151.71(3)°]. A nine‐membered zirconoxacycle complex Cp(O2C6H4NCHC6H4‐2O)ZrCl2 (6) can be obtained by an intramolecular elimination of CH3Cl from complex 1 or by the reaction of CpZrCl3·DME with dilithium salt of ligand. When activated by excess methylaluminoxane (MAO), complexes 1–6 exhibit high catalytic activities for ethylene polymerization. The influence of polymerization temperature on the activities of ethylene polymerization is investigated, and these complexes show high thermal stability. Complex 6 is also active for the copolymerization of ethylene and 1‐hexene with low 1‐hexene incorporation ability (1.10%). Copyright © 2006 John Wiley & Sons, Ltd.